Feel free to reduce CT dose when diagnosing pulmonary embolism

Clinicians can reduce the “tube voltage” (kVp) in CT pulmonary angiography without reducing image quality, according to a study published in the Journal of the American College of Radiology. Researchers from several Chicago-area universities and hospitals conducted a retrospective study to measure CT pulmonary angiography image quality as tube voltage was lowered, taking into account patient size as well as the benefits of simple image post-processing.

Concern over patient dose has been never been higher, especially for CT. That said, CT is an invaluable tool in many situations, especially in the diagnosis of pulmonary embolism.

If left undiagnosed, most patients will die within a few hours, underscoring the need for speed. CT pulmonary angiography allows a rapid diagnosis with high sensitivity and specificity, making it the first-choice imaging when a patient presents with embolism symptoms.

However, chest CT is especially harmful to patients when compared to head or abdomen CT, for example, because the lungs readily absorb radiation. One of the simplest ways to reduce CT dose is to lower the tube voltage, but the increased image noise can lower diagnostic confidence, especially in larger patients. It raises the question: how low can you go?

The researchers collected scans from June 2015 to June 2016, finding no statistically significant drop in image quality as they reduced the tube voltage—even for larger patients.

“Our study demonstrates that if the tube voltage is reduced from 120 to 80 kVp, the radiation dose is reduced by about 80%, which is consistent with the literature,” the authors wrote. “At the same time, there was no decrease in subjective image quality rated by a blinded reader or in objective image quality measured by the attenuation of the MPA.”

In addition, the use of simple, widely available post-processing mitigated up to 21 percent of the image noise across patient sizes, assuaging one of the primary fears of reducing tube voltage. Researchers overlapped images to create a clearer picture, and posited that recent hardware and software developments could further reduce image noise.  

The authors noted several limitations of the study, including a small amount of 80 kVp cases and non-standardized tube-time, but they stand by the viability of the research.

“Reducing tube voltages in CT pulmonary angiography results in significantly lower radiation dosages, while also improving both objective and subjective measures of image quality, despite increased image noise,” they wrote.